Streamer Duration combines the challenge of building a light
rocket that can fly high (to a good altitude to descend from), with a
streamer that can slow the descent as much as possible for a good duration
time.

In Streamer Duration, the model has to remain in one piece throughout
the flight and cannot be staged.

Multi-Round - This form of duration scoring involves
"Max" times and three flights. For B Streamer, the maximum time
is 180 seconds. As an example, if the model stays in the air for 216
seconds, it's official time is 180 seconds. However, 180 seconds is a hard
to reach max time for models powered by 18mm black powder B engines (the
only B's currently contest certified), even 120 seconds is difficult
without major help from thermal activity.

Models in multi-round scored events DO NOT have to be returned,
but only two models are allowed. This means that you need to return one
model to make your third flight . And if you make it to a flyoff, you'll
need a returned model for the fourth flight round.

Scoring - For Multi-Round Streamer Duration, the scoring is the
sum of all of the qualified flights. If there is a tie for first place at
the end of round three (normally three maxes), there will be a fly-off
round between those contestants who are tied, with the max time increased
by at least 60 seconds.

Design considerations - There are trade-offs between the model's
performance and the streamer's size. Low-mass and low-drag models may not
be strong enough to survive boost. Increasing the size of the streamer
means the streamer will need more room inside your rocket. A bigger
streamer is also heavier, which could weigh down the model too much.

Streamers - Streamer choice and preparation is important. Simple
crepe paper just doesn't do it. Some people use a certain grade of tracing
paper, while others prefer to use 1 mil Mylar. The tracing paper can
perform well, but also can rip more easily than other materials. So, 1 mil Mylar
is recommended. For B power, 6" by 60" streamers are a good size.

The trick to good performance out of the streamers is to put folds into
them. The folds improve the "whip" action of the streamers.
Some people use simple accordion type folds, or pleated folds, with the
folds spaced about 1/2" apart or so. Others roll the streamer up on
a 3/16" dowel, slide the rolled streamer off, then squash the rolled
streamer flat to give it folds that run the same way, as opposed to
zigzag accordion pleats. In any case, just pressing the folds is not good
enough for Mylar streamers, the folds will not set as well as desired for
good performance. Heat from an iron is needed. Either use an old iron or
apply some scrap cloth over the iron to protect the iron. Lay the iron
over the folded or rolled/flattened streamer and let it heat as deeply as
possible for many minutes. After you are done, place the streamer under
some heavy object to keep the folds tight while it cools off.

Shock Cords - Kevlar Shock cords of 100 pound grade are
recommended. Use a 3 to 4 feet length from the main body to the streamer.
Attach the cord securely to the streamer so that it cannot come off. Many
people like to use a 1" wide piece of tape folded across the bottom
of the streamer, trapping the shock cord. But the cord could still slip
free, so put a few knots into the portion of the cord that will be under
the tape. The adhesive tape should be a type that will not rip easily,
not scotch tape or masking tape. For extra strength, you can add a piece
of 1/2" wide strapping tape as shown.

Tips and info from other sources:

A Must-Read
Lecture article (.pdf) on building and flying Streamer/Parachute Duration,
written by Pavel Pinkas of the WOOSH section. Lots of useful
all-around information for flying Streamer Duration and Parachute
Duration.